This invention relates to a recording/reproducing apparatus for writing and/or reading out information signals on or from a disc-shaped recording medium, such as a read-only optical recording medium, known as a CD-ROM, an overwrite type optical recording medium or an optical recording medium which may be overwritten by light modulation or magnetic field modulation.
In a recording/reproducing apparatus, such as an optical disc player, a disc-shaped recording medium, referred to herein as an optical disc, is employed as an optical recording medium for information signals. Information signals are recorded on or reproduced from the signal recording area of the optical disc.
Among various sorts of optical discs, there is a special type CD-ROM, that is CD-R, having a signal recording area for writing information signals on the inner peripheral portion of the signal recording region of the disc. The CD-R has a signal recording area, about 1.8 mm in width, on a further inner side of the inner most portion of the signal recording region of the common CD-ROM. Consequently, with the recording/reproducing apparatus for the CD-R, it is necessary to move an optical pickup device towards a further inner side by about 1.8 mm than in the case of the CD-ROM.
Referring to FIGS. 1 and 2, a recording/reproducing apparatus 20 proposed by the present assignee is now explained. The recording/reproducing apparatus 20 for the optical disc has an optical pickup 33 for moving an objective lens 38 provided on a bobbin 35 with respect to the signal recording region of the optical disc.
The recording/reproducing apparatus 20 for the optical disc is roughly comprised of the optical pickup device 33, and a guide shaft 45 and a guide member 46 for assembling the optical pickup device 33. The apparatus 20 also includes a spindle motor 53 for running the optical disc in rotation, and a chassis member 51 carrying the guide shaft 45, guide member 46 and the spindle motor 53.
The optical pickup device 33 includes the objective lens 38, the bobbin 35 carrying the objective lens 38 and a mounting base 36 carrying the bobbin 35. The optical pickup device also includes a driving part 41 assembled on the mounting base 36, and the guide shaft 45 and the guide member 46 mounted on the chassis member 51 carrying the optical pickup device 33.
The chassis member 51 has a first supporting member 47A and a second supporting member 47B between which are carried both ends of the guide shaft 45. The chassis member 51 also has a first supporting member 48A and a second supporting member 48B between which are carried both ends of the guide member 46 so that the guide member runs parallel to the guide shaft 45. The optical pickup device 33 is slidably mounted on the guide shaft 45 and the guide member 46.
The mounting member 36 is formed of a metal material in a substantially rectangular shape and carries a bobbin 35 on its major surface. The mounting base 36 has sleeve mounting portions 40A, 40B as-one with its one end portion, and a sleeve member 54 is mounted on theses sleeve mounting portions 40A, 40B. The mounting base 36 is slidably mounted on the guide shaft 45 via the sleeve member 54.
The mounting base 36 has on its opposite end a lug 55 adjacent to the bobbin 35 and a supporting shaft 56 is provided on a lateral surface of the lug 55. The supporting shaft 56 rotatably carries a roll bearing 39 by means of which the mounting base 36 is slidably mounted via the roll bearing 39 on the guide member 46.
The mounting base 36 carries, on its lateral surface, a driving circuit 41 for driving the bobbin 3. The driving circuit 41 is connected to a power supply section, not shown, via a flexible cable 42. The mounting base 36 has an electro-magnetic floating unit 48 adjacent to the guide shaft 45, and a magnetic force is generated in the electro-magnetic floating unit 48 by the electric power furnished from the driving circuit 41. The chassis member 51 is provided with a first magnet member 52A and a second magnet member 52B parallel to the guide shaft 45.
That is, the optical pickup device 33 is moved in a state of being floated under a repulsive force generated by a magnetic force generated by the electro-magnetic driving unit 48 and a magnetic force generated by the first magnet member 52A and the second magnet member 52B provided in register with the electro-magnetic floating unit 48.
The bobbin 35 has the objective lens 38 and is flexibly supported by a hi-axial actuator. That is, the bobbin 35 has means for adjustment in the track direction, that is in a direction parallel to the signal recording region of the optical disc, and means for adjustment in a direction normal to the signal recording region.
With the above-described recording/reproducing apparatus 20 for the optical disc, the operation of moving the optical pickup device 33 for reading out information signals of the optical disc is now explained. The mounting base 38 is supported by the guide shaft 45 and by the guide member 46 while the mounting base 36 is floated by the electro-magnetic floating unit 48. The mounting base 36 is moved via the sleeve member 54 along the guide shaft 45 and the guide member 46.
By such movement of the mounting member 36, the optical pickup device 36 is moved along the radius of the optical disc for reading out and reproducing information signals on the optical disc. The optical pickup device 33 is halted when it is moved as far as the inner most portion of the signal recording region of the optical disc and the sleeve member 54 provided on the mounting base 36 has its one end abutted against an abutment 57A.
The optical pickup device 33 is also halted when it is moved as far as the outer most portion of the signal recording region of the optical disc and the sleeve member 54 provided on the mounting base 36 has its one end abutted against an abutment 57B. That is, with the recording/reproducing apparatus 20 for the optical disc, the range of movement of the optical pickup device 33 is delimited by the abutments 57A and 57B.
In addition, with the present recording/reproducing apparatus 20 for the optical disc, the objective lens 38 has its optical axis positioned with respect to the mounting base 36, when mounting the optical pickup 33, by way of effecting alignment adjustment. This alignment adjustment of the optical axis of the bobbin 35 is explained by referring to FIG. 2.
With the bobbin 35 being mounted on the mounting base 36, the sleeve member 54 of the mounting base 36 is mounted on the guide shaft 45. In this state, alignment adjustment, such as skew adjustment, is carried out for adjusting the tilt of the objective lens 38 with respect to the major surface, which is a signal recording region of the optical disc, with a lateral surface thereof adjacent to the optical axis of the objective lens 38 as a reference surface 37. Consequently, with the alignment-adjusted optical pickup device 33, an extremely precise relative position is maintained between the reference surface 37 and the optical axis of the objective lens 38.
With the above-described optical pickup device 33, it is necessary to prohibit the optical pickup device 33 from being abutted against a winding coil, not shown, provided on the spindle motor 53 adapted for running the optical disc in rotation, when the optical pickup device is moved towards the inner peripheral portion of the signal recording region of the optical disc. Thus the present optical pickup device 33 has its range of movement restricted so that, when it is moved towards the inner periphery of the signal recording region of the optical disc, it is halted ahead of the spindle motor 53.
That is, the optical pickup device 33 is provided with the abutment 57A in the vicinity of one end of the guide shaft 45 for restricting the sphere of movement thereof along the guide shaft 45 and the guide member 46. The optical pickup device 33 is halted by the sleeve member 54 provided on the mounting base 36 slid along the guide shaft 45 being abutted against the abutment 57A.
There is also known a method for halting the optical pickup device 33 by utilizing one lateral surface of the mounting base 36, that is by this lateral surface being caused to bear against an abutment provided on the chassis, as disclosed in U.S. Ser. No. 08/1252,069, filed on Jun. 1, 1994 as a continuation of U.S. Ser. No. 07/989,356 filed on Dec. 11, 1992, now abandoned, corresponding to EP Application 546,543, published on Jun. 13, 1994. However, with the above-described methods, it is difficult to maintain a correct relative position between the optical axis of the objective lens 38 of the optical pickup device 33 and the abutment 57A, such that a significant error tends to be produced in this relative position.